Single-Exposure HDR CMOS Pixel Charge Amplifier Design
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Solution Overview
Problem
Conventional large area CMOS image sensors face challenges with high power consumption, complex circuitry, reduced pixel fill-factor, and sensitivity to signal noise, particularly in high dynamic range (HDR) applications like medical X-ray imaging, where achieving low noise and high linearity is crucial.
Innovation Solution
A single-exposure HDR CMOS image sensor design utilizing a charge amplifier with two or more charge-to-voltage conversion capacitors for multi-phase readout, implementing a common-source configuration to maximize pixel fill-factor and reduce power consumption, along with a partially pinned photodiode structure for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If pixel level amplifiers are formed in an integrator configuration with a current source per integrator, then amplification capability is improved, but power consumption becomes too high for practical large pixel array applications
Solution Approach 1:
The patent combines multiple functions into a single charge amplifier circuit: charge-to-voltage conversion, signal amplification, and HDR imaging capability are all integrated into one pixel-level circuit. This eliminates the need for separate current sources per pixel, significantly reducing power consumption while maintaining amplification capability.
Solution Approach 2:
The charge amplifier is designed to perform multiple functions: it converts charge to voltage, provides signal amplification, enables high dynamic range imaging through dual gain modes, and operates across different lighting conditions. This multi-functionality reduces the need for additional dedicated circuits, lowering overall power consumption.
2Power
If complex circuitry and control signals are used in charge amplifiers, then amplification performance is improved, but production yields are degraded and profitability is reduced
Solution Approach 1:
The patent implements different gain modes (high gain and low gain) within the same charge amplifier circuit by selectively connecting different capacitors, rather than using completely different circuit topologies. This local differentiation maintains high performance while using a unified, manufacturable circuit design that simplifies production.
Solution Approach 2:
The patent achieves different amplification performance levels by changing the effective capacitance value in the charge-to-voltage conversion stage, rather than changing the fundamental circuit architecture. This parameter-based approach maintains circuit simplicity and ease of manufacture while providing versatile performance.
3Power
If complex circuitry is used in charge amplifiers, then amplification performance is improved, but pixel fill-factor is reduced and SNR is degraded
Solution Approach 1:
The patent segments the charge amplifier functionality into distinct operational modes (high gain mode using C1, low gain mode using C2) that share the same physical circuit infrastructure. This segmentation allows the circuit to achieve high performance when needed while maintaining a compact footprint that preserves pixel fill-factor.
Solution Approach 2:
The patent uses dynamic switching between different capacitor configurations to achieve different gain modes, allowing the circuit to adapt its performance characteristics in real-time without requiring multiple static circuit implementations. This dynamic approach maximizes pixel fill-factor while maintaining amplification performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables high dynamic range imaging with reduced motion artifacts and lower X-ray dose exposure, achieving high-end analog performance with minimized noise and increased frame rate while maintaining low cost and high resolution.
Implementation Method 1
Each pixel includes a sensing element (e.g., a photodiode) that is capable of converting a portion of an optical (or other radiant source) image into an electronic (e.g., voltage) signal
Implementation Method 2
each pixel utilizes a charge amplifier having two or more different charge-to-voltage conversion capacitors that are used to measure a single photodiode charge
Data Source
AI summary
A single-exposure high dynamic range (HDR) image sensor utilizes a charge amplifier having two different charge-to-voltage conversion capacitors that read a single photodiode charge during a two-phase readout operation. The first capacitor has a lower capacitance and therefore higher conversion gain (sensitivity), and the second capacitor has a higher capacitance and therefore lower conversion gain (sensitivity). The two-phase readout operation samples the photodiode charge twice, once using the high sensitivity capacitor and once using the low sensitivity capacitor. The high sensitivity readout phase provides detailed low light condition data but is saturated under brighter light conditions, and the low sensitivity readout phase provides weak data under low light conditions but provides high quality image data under brighter light conditions. The final HDR image is created by combining both high and low sensitivity images into a single image while giving each of them the correct weighted value.